The present invention relates to the structure of a ferrite core, in particular, relates to such a core for the use of a transformer and/or a choke coil in a power supply circuit. The present ferrite core is utilized for a transformer and/or a choke coil in a power supply circuit in electric appliances up to 1 kW.
When the present core is utilized for a power transformer a primary power supply is applied to the transformer through a switching circuit operating by a DC power supply applying an alternate current input to the transformer, and thus, the desired secondary voltage is obtained at the output of the transformer.
When a ferrite core is utilized for a power transformer, that core must at least satisfy the following conditions.
(a) A core must not magnetically saturate, and preferably, the cross section along the magnetic path is identical for the whole magnetic path in the core.
(b) A core is preferably closed by itself for improving the shield effect for not disturbing an external circuit.
(c) The shape of a core is preferably simple, and a bobbin having windings can be easily mounted in a core, and lead wires of windings can extend easily outside of a core.
(d) A core must satisfy the lawful safety standard for a power supply circuit issued in each country. The safety standard requests for instance the minimum duration between pins, the minimum duration between a core and a pin, et al.
(e) A core must be small in size, and light in weight. And the output power of a transformer for each unit weight(gr) is as large as possible.
(f) Preferably, the external shape of a core is rectangular for saving the mounting area of the transformer on a printed circuit board, and the shape of the central core is circular for the sake of the winding.
(g) The manufacturing process of a core is simple, and a core is mechanically strong. If a core has a sharp or edged portion, that portion will be broken easily.
The most popular conventional ferrite core is in E-shaped with the identical cross section, or alternatively, a combination of the E-shaped core and the I-shaped core is utilized. However, that core has the disadvantages that the size is large, the shield effect is not perfect, and further since a bobbin must be rectangular, windings are folded and thus, the insulation is not sufficient and the automatic winding is impossible.
Another conventional ferrite core is a so-called pot core which has a closed outer wall and a center core mounted at the center of the wall. Although a pot core is excellent in the shield effect, that pot core has the disadvantage that it is difficult to extend lead wires of windings outside, since a slit for accepting lead wires is too small in that pot core.
Another prior ferrite core is shown in UK patent No. 1306597 which has a pair of thick diametrically opposed outer legs. That core is proposed for the use in a high frequency filter, but is not suitable for a power supply transformer, since the shield effect is poor, and the size is large.
Another prior ferrite core is shown in UK patent No. 1169742 which has four legs and the center core at the center of those legs. Although that core is advantageous to extend lead wires to an external circuit through the wide window between legs, that core has the disadvantage that the core is apt to saturate at the leg portions, since those legs are rather thin. Therefore, that core is advantageous for the use of the high output voltage application, but is not suitable for a power supply transformer.
Another prior ferrite core is the modification of a so-called pot core, and a pot core is separated into two substantially U-shaped portions. This shape is preferable to improve the shield effect, but has the disadvantage that it is difficult to connect lead wires to an external circuit.
Still another prior ferrite core has the wide disk between the center core and the outer walls. However, in this core, the structure of a bobbin is rather complicated, and the core is apt to saturate, thus, that core is not suitable for the use of a high power transformer.